Wine is traditionally defined as an alcoholic beverage produced when fruit undergoes primary fermentation in which yeast converts the sugar in fruit to alcohol. When the sugar supply is exhausted, the yeast dies off, leaving the alcohol produced to blend with, or attach to, other components.
Almost all wine improves with aging. However, peak flavor and bouquet may require years to develop in wines with high concentrations of tannins, and many wines deteriorate not long after reaching their peak. Chemical reactions during the aging process are extremely complex and well documented. The desirable characteristics of wine result from a blending of the components in the wine.
Wines without high concentrations of tannins develop flavor and bouquet more rapidly. These wines may also deteriorate not long after reaching their peak.
The traditional wine aging process is simple, well known, and well understood. Oxidation is among the greatest problems with which a winemaker deals during the making and aging process for wine. Oxidation can adversely affect the fruity flavor and freshness of wine. In order to prevent oxidation of the wine, sulfur dioxide (as potassium metabisulfite or sodium metabisulfite) is frequently added to grape must before fermentation to inhibit or kill all unwanted bacteria prior to the point at which the alcohol production commences after fermentation begins. The metabisulfite salts are converted to sulfur dioxide, which is the so-called “free sulfite” of wine. After fermentation produces some alcohol, the sterilizing effects of alcohol assist in killing the unwanted bacteria.
In some wines, particularly those of the Sauternes type, a considerable quantity of naturally-occurring sulfur dioxide is retained in the wine until the wine is bottled. In red wines and in some white wines, sulfur dioxide is added to prevent the wine from becoming unsound.
When sulfur dioxide is first added in the free state, it rapidly combines with other substances in the wine, so that sometimes in a few minutes, and, in other cases, in as much as thirty minutes, the amount of free sulfur dioxide is halved. Over a period of weeks or months, the exact rate of disappearance depends upon many factors, such as temperature and amount of aeration, whereby the total sulfur dioxide content of the wine falls.
During the normal aging process for wine, the conditioners and preservatives, such as sulfur dioxide, are dispersed throughout the liquid. Changes in the wine following bottling are subtle and difficult to establish, since there are no measurements other than taste and smell that are used to determine when the aging process is complete and when the wine invariably begins its decline. Further, the ingredients used vary among wines and winemakers, and each ingredient may affect the aging process differently.
There is a direct relation between the amount of sulfite added and the inhibition of bacterial growth in wine. As such, large scale wine producers, whose risks are high, may use a relatively high concentration of additives such as sulfite to avoid spoilage. However, with the addition of large amounts of sulfites, the wine can be adversely affected, irrespective of the lack of bacterial deterioration.
Some smaller wine producers advertise that they do not use sulfite. This is important to many consumers, as some consumers complain of headaches which are attributed to the presence of sulfite in wines, even though all wines contain a small amount of naturally occurring sulfites. Although the relationship between sulfites in wine and headaches has not been clinically confirmed, many believe that the link is real. As such, wines not containing added sulfites may command a higher retail price, because manufacturing costs are higher and the risk of losing entire batches of wine to bacterial contamination and/or oxidation is borne by the consumer.
Although all wines naturally contain some sulfites as a result of the fermentation process, the amounts of these sulfites are not noticeable to most people. However, when sulfites are added to the must, during fermentation and more so after bottling, gaseous hydrogen sulfide develops in the wine. This gas is extremely toxic and, in many cases, may destroy what would otherwise be a good wine. The concept of decanting the wine, or letting the wine “breathe”, in essence allows the hydrogen sulfide to volatilize out of the wine so that it is then suitable for drinking. There is no nutritional value to the sulfites added to wine, and, in the case of sodium metabisulfite, consumers may wish to avoid additional sodium as well.
Red wine contains a number of antioxidant polyphenols, which scavenge free radicals and up-regulate certain metal chelation reactions. The polyphenols can reduce inflammatory effects such as coronary artery disease and can inhibit the growth or occurrence of mammalian tumors.
Consuming dietary polyophenols may be associated with beneficial effects in higher animal species, including reduction in inflammatory effects such as coronary artery disease, including improved endothelial health via down-regulation of oxidative LDL and anti-aging consequences such as slowing the process of skin wrinkling.
A high intake of polyphenols is likely to have beneficial effects on the cardiovascular system. Red wine is a rich source of polyphenols, and it has been demonstrated that trans-resveratrol, 3,4′,5-trihydroxy-trans-stilbene, has been found to be the most efficacious stimulator of eNOS expression, which enzyme is protective of the cardiovascular system. However, the presence of resveratrol alone could not explain the total stimulatory effect of red wine. The flavanols catechin and epicatechin, the flavanols fisetin, myricetin, isoquercetin and hyperoside, the anthocyanins delphinidin, malvidin and paeodnidin, gallic acid, and the hydroxycinnamic acids ferulic acid and sinapinic acid did not change eNOS expression or eNOS promoter activity in any substantial way. The anthocyanin cyanidin, the hydroxycinnamic acids p-coumaric acid and caffeic acid, and the phenolic acids benzoic acid and vanillic acid also enhanced eNOS expression moderately. Thus, the increase in eNOS in response to ingestion of red wine involves several polyphenolic compounds, with trans-resveratrol making a major contribution, and lesser contributions from cinnamic and hydrocinnamic acids, cyaniding and some phenolic acids. [Nitric Oxide, 2005, 12(2):97-104]
Sulfur dioxide has been shown to interact with polyphenols and oxygen in wine, which reaction is catalyzed by the presence of copper and iron, which are naturally found in wine grapes Danielewicz, Am. J. Enol. Vitic. 58(1): 53-60 2007.